Photograph: Kate Whitaker
Preheat the oven to 200°C, fan 180°C, gas 6. For the pesto, spread out the walnuts on a baking tray and bake for 6 minutes or until toasted. Transfer the walnuts to a food processor, add the rest of the pesto ingredients and season well. Whiz until smooth, then transfer to an airtight container with a lid and set aside.
Chop the leeks finely. Heat the butter and oil together in a large heavy-based sauté pan. Add the leeks and fry over a gentle heat for 6-8 minutes until soft. Stir in the thyme leaves, then add the rice and ‘toast' it for a few minutes, stirring constantly. Add the wine, bring to the boil and allow it to reduce for a few minutes.
Add the hot stock a ladleful at a time, stirring constantly and waiting until a crescent-moon shape appears at the bottom of the pan before adding the next ladleful. Continue stirring ladlefuls of stock into the rice until the rice is almost cooked, but the grains are slightly al dente – this will take about 25 minutes. You may have stock left over; just use as much as you need.
Stir in the cheese and season to taste, then immediately remove the pan from the heat and cover with a lid. Leave to stand for a couple of minutes before serving in warmed bowls, topped with a spoonful of pesto.
Recipe adapted from The Italian Cookery Course by Katie Caldesi (Kyle Books, £19.99)